Hot air knives have been employed for increasing the integrity of nonwoven webs such as spunbonded filament webs. A hot air knife is useful in bonding the individual polymer filaments together at various locations, so that the web has increased strength and structural integrity. Hot air knives are also used for aligning meltblown fibers during manufacture of meltblown webs, for cutting nonwoven fabrics, for chopping reclaim, and for a variety of other uses.
One use of the hot air knife is to improve the structural integrity of nonwoven webs before passing them through standard inter-filament bonding processes. Through-air bonding ("TAB") is a process of bonding a nonwoven bicomponent fiber web in which air sufficiently hot to melt one of the polymers in the fibers of the web is forced through the web. The air velocity is between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides the bonding.
A conventional hot air knife includes a mandrel with a slot that blows a jet of hot air onto the nonwoven web surface. U.S. Pat. No. 4,567,796, issued to Kloehn et al., discloses a hot air knife which follows a programmed path to cut out shapes needed for particular purposes, such as the leg holes in disposable diapers. U.S. Pat. No. 5,707,468, issued to Arnold et al., discloses using a hot air knife to increase the integrity of a spunbond web. U.S. application Ser. No. 08/877,377 to Marmon et al., filed Jun. 17, 1998, discloses a zoned hot air knife assembly used to heat discrete portions of a nonwoven web.
It is also known to use heat to facilitate the uniform migration of internal additives from nonwoven webs. U.S. Pat. Nos. 4,857,251, 4,920,168, 4,923,914, and 5,120,888, all issued to Nohr et al., disclose using heat to facilitate the migration of internal additives to the surfaces of nonwoven webs.